DE69318528T2 - TWO-STAGE OF FREE RADICAL CATALYZED METHOD FOR PRODUCING ALKENYLSBERSTIC ACID ANHYDRIDE - Google Patents

Description

BACKGROUND OF THE INVENTION

The invention relates to a process for the preparation of compositions which are suitable as intermediates for dispersants used in lubricating oil compositions or as dispersants themselves. In addition, some of the compositions prepared by the process according to the invention are suitable for the preparation of high molecular weight dispersants which have better dispersing properties for sludge and varnish. These high molecular weight dispersants also advantageously impart fluidity-modifying properties to the lubricating oil compositions, so that some of the viscosity number improvers can be omitted from multigrade lubricating oil compositions containing these dispersants.

Alkenyl-substituted succinic anhydrides are, as is well known, used as dispersants. The alkenyl-substituted succinic anhydrides are prepared by two different processes, a thermal process (see, for example, U.S. Patent 3,361,673) and a chlorination process (see, for example, U.S. Patent 3,172,892). The polyisobutenyl succinic anhydride ("PIBSA") prepared by the thermal process is characterized as a monomer having one double bond in the product. The exact structure of the chlorination PIBSA has not yet been definitively determined. However, the PIBSA masses from the chlorination process are characterized as monomers containing in product either a double bond, a ring which is not a cyclic succinic anhydride, and/or chlorine [See J. Weill and B. Sillion, "Reaction of Chlorinated Polyisobutene with Maleic Anhydride: Mechanism Catalysis by Dichloromaleic Anhydride", Revue de l'Institut Francais du Petrole, Vol. 40, No. 1, pp. 77-89 (January-February 1985)]. Such compositions contain 1:1 monomer adducts (see, for example, U.S. Patents 3,219,666 and 3,381,022) as well as adducts containing at least 1.3 succinic anhydride groups per polyalkenyl-derived substituent (see, for example, U.S. Patent 4,234,435).

International patent application PCT/US89/04270 (Publication No. WO 90/03359, filed April 5, 1990, entitled "Novel Polymeric Dispersants Having Alternating Polyalkylene and Succinic Groups") describes copolymers prepared by reacting an unsaturated acidic reactant such as maleic anhydride with a high molecular weight olefin such as polyisobutene in the presence of a free radical initiator. The total high molecular weight olefin consists of at least about 20% of an alkylvinylidene isomer. The high molecular weight olefin has enough carbon atoms that the resulting copolymer dissolves in lubricating oil.

U.S. Patent 4,234,435 (Meinhardt et al., assigned to The Lubrizol Corporation) discloses substituted succinic acylating agents derived from polyalkenes such as polybutene and a dibasic carboxylic acid reactant such as maleic acid or anhydride, wherein the polyalkenes have a number average molecular weight of about 1300 to 5000 and a weight average molecular weight to number average molecular weight ratio of about 1.5 to 4. These acylating agents are further characterized by having an average of at least 1.3 succinic groups per equivalent weight of substituent group. These acylating agents are referred to as Meinhardt et al. by heating the polyalkene and the carboxylic acid reactant with chlorine in a one-step process or, alternatively, by first reacting the polyalkene with chlorine and then reacting the resulting chloropolyalkene with the carboxylic acid reactant. The patent also teaches that these substituted succinic acylating agents and their derivatives are useful lubricating oil dispersant additives that also exhibit viscosity index improving properties.

US Patent 4,873,004 (Beverwijk et al., assigned to Shell Oil Company) discloses an alkyl- or alkenyl-substituted succinic anhydride, wherein the alkyl or alkenyl radical on the anhydride has a number average molecular weight of 600 to 1300 and the average number of succinic acid groups per alkyl or alkenyl radical is between 1.4 and 4.0. Beverwijk et al. teach that these alkyl or alkenyl substituted succinic anhydrides can be prepared by mixing a polyolefin with maleic anhydride and passing chlorine through the mixture or by reacting a chlorinated polyolefin with maleic anhydride. Beverwijk et al. also teach that the succinimide derivatives of these substituted succinic anhydrides are useful dispersant additives for lubricating oils.

U.S. Patent 3,367,864 (Elliot et al., assigned to Castrol Limited) discloses in Example 1 the preparation of a polyisobutenyl succinic anhydride wherein polyisobutylene and maleic anhydride are reacted in a molar ratio of about 1:1 under reflux of toluene and in the presence of a di-tert-butyl peroxide radical initiator. Elliot et al. also teach that the succinic anhydride product produced in this process is similar to the product obtained by thermally reacting polyisobutylene and maleic anhydride at 240°C for 30 hours.

Those skilled in the art will appreciate that polyisobutenyl succinic anhydride prepared by a conventional thermal process is predominantly a monomeric 1:1 adduct, i.e., the product contains approximately one succinic acid group per polyisobutenyl radical. Recent studies of polyisobutenyl succinic anhydride products prepared by the free radical initiator process of Example 1 of U.S. Patent 3,367,864 indicate that these products are monomer adducts containing an average of about 1.6 or more succinic acid groups per polyisobutenyl radical.

European patent application 0 355 895 A2 (published on February 28, 1990) discloses a process for preparing polyolefin-substituted succinic anhydrides in which the average molar ratio of succinic groups to polyolefin chains is greater than 1.3:1. It comprises heating a polyolefin with at least a molar excess of maleic anhydride, wherein at least 70% of the terminal groups of the polyolefin used are in a structure with an alpha-olefinic bond or in structures that are in equilibrium with these alpha-olefinic structures. This European patent application teaches that more than 1.3 succinic acid groups per polyolefin residue can be obtained if the predominant isomer of the polyolefin used is an alkylvinylidene.

SUMMARY OF THE INVENTION

The invention provides a two-step process for preparing an alkenyl-substituted succinic anhydride wherein the number average molecular weight of the alkenyl substituent is 500 to 5000 and the average number of succinic groups per alkenyl radical is greater than 1.2, comprising:

(a) reacting a polyolefin containing less than 10 percent alkylvinylidene isomers and having a number average molecular weight of from 500 to 5000 with maleic anhydride in the presence of a free radical initiator at a temperature of from 100°C to 220°C to provide a mixture of alkenylsuccinic anhydride having an average of more than 1.2 succinic groups per alkenyl group and unreacted polyolefin, with conversion of the polyolefin occurring at from about 30 to about 65 percent, and

(b) reacting the mixture of alkenyl succinic anhydride and polyolefin with maleic anhydride at a temperature of 200°C to 250°C to provide an alkenyl succinic anhydride having an average of more than 1.2 succinic groups per alkenyl radical and the total conversion of the polyolefin is 5 to 40 percentage points higher than the conversion in step (a), wherein the alkylvinylidene isomer has the formula:

wherein R₁ is a lower alkyl group having 1 to 6 carbon atoms and R₂ is a polyolefin group.

The invention is based, among other things, on the discovery that certain alkenyl-substituted succinic anhydrides can be An average of more than 1.2 succinic acid groups per alkenyl residue can be produced in high yields and conversions by using, for the first time, a two-step process that does not use chlorine, thus obtaining an environmentally friendly product.

The average number of succinic acid groups per alkenyl radical in the alkenylsuccinic anhydride obtained according to the invention is above 1.2, preferably above 1.3, more preferably above 1.3 to 4.0 and most preferably above 1.3 to 2.5.

Polyolefins suitable for use in making the alkenyl succinic anhydride products have a number average molecular weight of from 500 to 5000, preferably from 700 to 3000, and more preferably from 900 to 2500. These polyolefins usually contain at least 35 carbon atoms, preferably 50 carbon atoms or more. The preferred polyolefins are polybutene and polypropylene, especially polyisobutene. The alkylvinylidene isomer content of a suitable polyolefin is less than 10%.

The succinic anhydride products produced by the process according to the invention are suitable as dispersants themselves and also as intermediates for the production of further dispersant additives which, when used in a lubricating oil, have better dispersing and/or detergency properties.

The products manufactured using the process according to the invention can also be used to manufacture polysuccinimides. These are produced by reacting the alkenylsuccinic anhydride with a polyamine. The polysuccinimides can be used as dispersants and/or detergents in fuels and oils. They also have advantageous viscosity-modifying properties and, when used in lubricating oils, provide a viscosity number reserve ("VI reserve"). In lubricating oils that contain these, a certain proportion of the viscosity number improvers ("VI improvers") can therefore be omitted.

The succinic anhydrides produced by the process according to the invention can also be used in the production of modified polysuccinimides in which one or more nitrogen atoms of the polyamine component are substituted with a hydrocarbonoxycarbonyl, a hydroxyhydrocarbonoxycarbonyl or a hydroxypoly(oxyalkylene)oxycarbonyl radical. These modified polysuccinimides are used as better dispersants and/or detergents in fuels or oils.

The alkenyl succinic anhydrides prepared by the process of the invention are thus suitable for providing a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and an amount of a succinic anhydride, a polysuccinimide or a modified succinimide additive sufficient to provide dispersibility and/or detergency. These additives can also be formulated into lubricating oil concentrates containing 10 to 50% by weight of additive.

The alkenyl succinic anhydrides prepared by the process of the present invention can be used to provide a fuel composition comprising a major proportion of a gasoline or diesel range boiling fuel and an amount of a succinic anhydride, polysuccinimide or modified succinimide additive sufficient to provide dispersibility and/or detergency. These additives can also be used to prepare fuel concentrates comprising an inert stable oleophilic organic solvent boiling in the range of 65.6°C (150°F) to 204.4°C (400°F) and 5 to 50 weight percent of the additive.

DETAILED DESCRIPTION OF THE INVENTION

The high molecular weight polyolefin chains used in the preparation of the alkenylsuccinic anhydrides according to the invention are sufficiently long that the resulting composition is soluble in and compatible with mineral oils and fuels. The polyolefin therefore usually contains 35 Carbon atoms or more, preferably about 50 carbon atoms or more.

These high molecular weight polyolefins are usually mixtures of molecules of different molecular weights and have at least one branching of 6 carbon atoms, preferably at least one branching of 4 carbon atoms and more preferably one branching of 2 carbon atoms along the chain. These branched olefin chains can comprise polyalkenes which can be prepared by polymerizing olefins having 3 to 6 carbon atoms, preferably olefins having 3 to 4 carbon atoms and even better propylene or isobutylene. The addition-polymerizable olefins used are usually 1-olefins. The branching has 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms and is preferably methyl.

The polyolefins used in the process according to the invention can be prepared by conventional processes known in the art, for example by aluminum chloride-catalyzed polymerization of lower olefins.

The preferred polyolefins are polyisobutenes having a number average molecular weight of from 500 to 5000 and more preferably from 700 to 3000. Polyisobutenes having a number average molecular weight of from 900 to 2500 are particularly preferred.

The alkylvinylidene isomer content of the polyolefins used in the process according to the invention is low, ie less than 10% alkylvinylidene. The term "alkylvinylidene" or "alkylvinylidene isomer" here stands for olefins of the formula:

wherein R₁ is a lower alkyl having 1 to 6 carbon atoms and R₂ is a polyolefin radical. Alkylvinylidene polyolefins with a high alkylvinylidene content, ie more than 10%, such as the commercially available Ultravis type polyisobutene, are not suitable for use in the process according to the invention, because these materials form copolymers with maleic anhydride in the presence of a radical initiator.

The ratio of weight average molecular weight (MW) to number average molecular weight (MN), i.e. MW/MN, for the polyolefins used in the invention is in the range of 1.1 to 4.0. The MW and MN values for the polyolefins used in the invention are determined by gel permeation chromatography (GPC), as described, for example, in US Patent 4,234,435 (Meinhardt et al.).

The invention, as already mentioned, relates to a unique two-step process for producing an alkenyl succinic anhydride having more than 1.2 succinic groups per alkenyl radical, the first step involving reacting a polyolefin with maleic anhydride in the presence of a free radical initiator to produce a mixture of unreacted polyolefin and alkenyl succinic anhydride having an average of more than 1.2 succinic groups per alkenyl radical. The conversion of the polyolefin is 30 to 65 percent. In the second step, the mixture of unreacted polyolefin and alkenyl succinic anhydride from the first step is then reacted with additional maleic anhydride under thermal conditions such that the desired product having an average of more than 1.2 succinic groups per alkenyl radical is obtained and the overall conversion of the polyolefin is 5 to 40 percentage points higher than the conversion in the first step.

Thus, in the first step of the process of the invention, polyolefin and maleic anhydride are reacted in the presence of a free radical initiator. The temperature of this reaction usually ranges from 100°C to 220°C, preferably from 120°C to 180°C. The reaction time varies in part depending on the reaction temperature, but usually ranges from 2 to 30 hours, preferably 4 to 20 hours. The reaction pressure is atmospheric pressure. However, higher pressures up to 441.2 kPa (50 psig) are preferred. The molar ratio of maleic anhydride to polyolefin is usually from 1:1 to 9:1. This reaction usually produces a 30 to 65% Conversion of the polyolefin into an alkenyl succinic anhydride product with an average of more than 1.2 succinic groups per alkenyl residue.

In the second step of the process of the present invention, the crude reaction mixture of alkenyl succinic anhydride and unreacted polyolefin from the first step is reacted with additional maleic anhydride under thermal conditions. The temperature of this reaction is usually from 200°C to 250°C, preferably from 220°C to about 240°C. The reaction time is suitably from 2 to 10 hours, preferably from 4 to 8 hours. The reaction pressure is atmospheric pressure. However, higher pressures up to 441.2 kPa (50 psig) are preferred. Usually from 1 to 9 moles of maleic anhydride are used per mole of the mixture of alkenyl succinic anhydride and unreacted polyolefin from the first step. The maleic anhydride used in the second step is either an excess from the first step or additional maleic anhydride added. The reaction continues until a conversion of the polyolefin to the desired alkenyl succinic anhydride product is obtained that is 5 to 40 percentage points higher than the conversion in the first step.

The reaction involved in the first or second step of the process according to the invention takes place with or without a solvent that is inert to the reaction taking place. Suitable solvents that may be used include toluene, xylene, C9 aromatics and neutral oil. Preferably, both reactions are carried out without solvent.

The alkenyl succinic anhydride prepared by this two-step process contains an average of more than 1.2 succinic groups per alkenyl radical, preferably more than 1.3, more preferably more than 1.3 to 4.0, and most preferably more than 1.3 to 2.5 succinic groups per alkenyl radical.

The first step of the process according to the invention can usually be initiated with a radical initiator. These initiators are known in the art. The choice of radical initiator However, it depends on the reaction temperature used.

The half-life with which the radical initiator decomposes at the reaction temperature is preferably 5 min to 10 h, more preferably 10 min to 5 h, and most preferably 10 min to 2 h.

The preferred radical initiators are of the peroxide and azo type.

The peroxide type radical initiator is organic or inorganic. The organic one has the general formula: R₃OOR₃', where R₃ is an organic radical and R₃' is selected from the group consisting of hydrogen and any organic radical. R₃ and R₃' can be organic radicals, preferably hydrocarbon, aroyl and acyl radicals, optionally bearing substituents such as halogens. The preferred peroxides include di-tert-butyl peroxide, tert-butyl peroxybenzoate and dicumyl peroxide.

Examples of other suitable peroxides include, but are not limited to, benzoyl peroxide, lauroyl peroxide, other tert-butyl peroxides, 2,4-dichlorobenzoyl peroxide, tert-butyl hydroperoxide, cuminic hydroperoxide, diacetyl peroxide, acetyl hydroperoxide, diethyl peroxycarbonate and tert-butyl perbenzoate.

The azo-type compounds, e.g. α,α'-azobisisobutyronitrile (AIBN), are also known free radical initiator materials. These azo compounds can be defined as containing the -N=N group in the molecule, with the balance being provided by organic radicals, at least one of which is preferably attached to a tertiary carbon atom. Other suitable azo compounds include p-bromobenzenediazonium fluoborate, p-tolyldiazoaminobenzene, p-bromobenzenediazonium hydroxide, azomethane and phenyldiazonium halides. A suitable list of azo-type compounds can be found in U.S. Patent 2,551,813 (Paul Pinkney, published May 8, 1951).

The half-lives for known radical initiators at different temperatures are readily available from the literature, see for example C. Walling, "Free Radicals in Solution", John Wiley and Sons, Inc., New York (1957). However, the half-life values can also be obtained from the various suppliers of radical initiators, for example Witco, Atochem, Lucidol and Phillips Petroleum. Table 1 shows the half-life temperatures for several radical initiators for a given half-life. The half-life temperature is the temperature at which a radical initiator has a certain half-life. The higher the half-life temperature, the shorter the half-life of the radical initiator. TABLE 1 Half-life temperatures of various radical initiators at certain half-lives

The The amount of initiator to be used depends very much on the particular initiator selected, the olefin used and the reaction conditions. The initiator should usually be soluble in the reaction medium and is usually present in concentrations between 0.001:1 and 0.4:1 mole of initiator per mole of polyolefin reactant. The preferred amounts range from 0.005:1 to 0.20:1.

In carrying out the process of the invention, the free radical initiators can be used individually or in a mixture. For example, it would be desirable to add an initiator with a low decomposition temperature when the mixture is warmed to room temperature and then a initiator with a higher decomposition temperature when the mixture reaches higher reaction temperatures. Alternatively, a combination of initiators can be added before heating and reaction. In this case, the initiator with the high decomposition temperature is initially inert and only becomes active later when the temperature increases.

The starter can also be added gradually. For example, if a starter with a short half-life, e.g. 5-20 min, is added at the reaction temperature, this can be done over a period of time such that an appropriate concentration of free radicals is available during the reaction time, so that better yields of the desired product are obtained.

When the reaction is considered complete, for example by NMR analysis, the reaction mixture is usually heated to decompose the remaining initiator. This temperature is usually about 160ºC or higher for a di-(tert-butyl)peroxide initiator.

The term "multiple addition" refers here to the alkenylsuccinic anhydride reaction product of maleic anhydride and polyolefin, wherein more than one maleic anhydride molecule is bonded to a polyolefin molecule.

The average extent of multiple addition can be calculated from the saponification number (mg KOH per g sample), the content of active ingredients of the alkenylsuccinic anhydride product and the molecular weight of the starting polyolefin. The "average extent of multiple addition" is the average number of succinic groups per polyolefin residue in the alkenyl succinic anhydride product. For example, an average extent of multiple addition of 1.0 means that an average of one succinic group is present per polyolefin residue in the alkenyl succinic anhydride product. Similarly, an average extent of multiple addition of 1.35 means that an average of 1.35 succinic groups are present per polyolefin residue in the alkenyl succinic anhydride product, and so on.

The active ingredient content of the alkenyl succinic anhydride product is measured as active ingredient percentage, where an active ingredient percentage of 1.0 corresponds to 100% active ingredient. An active ingredient percentage of 0.5 corresponds to 50% active ingredient.

The average degree of multiple addition for the alkenylsuccinic anhydride product from maleic anhydride and polyolefin can be calculated using the following equation:

Average degree of multiple additions = MPO x P/(c x A) - (MMA x P)

where

P = saponification number of the alkenyl succinic anhydride sample (mg KOH/g);

A = proportion of active components of the alkenylsuccinic anhydride sample;

MPO= number average molecular weight of the starting polyolefin;

MMA= molecular weight of maleic anhydride;

C = Conversion factor = 112220 (for the conversion of gram- moles of alkenylsuccinic anhydride per gram of sample to milligrams of KOH per gram of sample)

The saponification number P can be measured using known methods, for example as described in ASTM D94.

The amount of active ingredients in the alkenylsuccinic anhydride can be determined from the percentage of unreacted polyolefin according to the following procedure. A 5.0 g sample of the reaction product of maleic anhydride and polyolefin is dissolved in hexane, applied to a column of 80.0 g of silica gel (Davisil 62, a 140 Å pore size silica gel) and eluted with 1 L of hexane. The percentage of unreacted polyolefin is determined by removing the hexane solvent from the eluent under vacuum and weighing the residue. The percentage of unreacted polyolefin is calculated using the following formula:

Percent of unreacted polyolefin = net weight of residue/sample weight x 100

The weight percent of active ingredients for the alkenyl succinic anhydride product is calculated from the percent of unreacted polyolefin using the following formula:

Weight percent active material = 100 - percentage of unreacted polyolefin

The proportion of active components of the alkenylsuccinic anhydride is then calculated as follows:

Active fraction = weight percent active ingredients/100

The percentage conversion of the polyolefin is calculated from the weight percent of the active ingredients as follows:

wherein

MPO= number average molecular weight of the starting polyolefin,

MMA= molecular weight of maleic anhydride,

MADD = Average Degree of Multiple Addition.

Of course, the alkenyl succinic anhydride products prepared by the process of the invention, in which the average multiple addition is high, can also be mixed with other alkenyl succinic anhydrides in which the multiple addition is lower, for example about 1.0, so that a succinic anhydride product with an intermediate average degree of multiple additions is obtained.

The following examples are intended to illustrate the invention in detail.

EXAMPLES example 1 Step (a)

2648 g (2.04 moles) of polyisobutene having a number average molecular weight of 1300 and a methylvinylidene isomer content of about 6% was charged to a reactor, heated to 150°C and stirred at 60 rpm with a mechanical stirrer. A mixture of 29.8 g (0.204 moles) of di-tert-butyl peroxide, 318 g of 100 neutral diluent oil and a total of 399.4 g (4.08 moles) of maleic anhydride was added over a period of four hours. The reaction was allowed to continue at 150°C for an additional hour. The resulting polyisobutenyl succinic anhydride product had a saponification number of 63.8 mg KOH/g sample, 45 wt.% active ingredients and an average of about 1.87 succinic groups per polyisobutenyl radical. The polyisobutene was about 41.8% The half-life of the di-tert-butyl peroxide radical initiator was about 1 hour at the reaction temperature of 150ºC.

Step (b)

4000 g of the polyisobutenyl succinic anhydride product obtained from two runs of the process described in step (a) and containing 55 wt. % unreacted polyisobutene were charged to a reactor. The temperature was raised to 232°C. 867 g (8.85 moles) of maleic anhydride were added over a period of 4.5 hours. The reaction pressure was maintained at 160.6 kPa (24 psia (9.3 psig)). The reaction was allowed to continue at 232°C for an additional 0.5 hour. The excess maleic anhydride was then removed under vacuum and the product filtered at 200°C. The resulting polyisobutenyl succinic anhydride product had a saponification number of 85.9 mg KOH/g sample, 71.4 wt. % active ingredients and an average of about 1.56 succinic groups per polyisobutenyl moiety. The polyisobutene was converted to about 69.1 percent. The total conversion after step (b) was thus 27.3 percentage points higher than the conversion in step (a).

Example 2 (comparison)

The example demonstrates that a radically initiated one-step process corresponding to step (a) of the invention results in a lower yield of the desired alkenyl succinic anhydride product than the unique two-step process of the invention.

61900 g (47.6 mol) of polyisobutene with a number average molecular weight of 1300 and a methylvinylidene isomer content of about 6% were placed in a reactor and heated to 150ºC. A mixture of 695.2 g (4.76 mol) of di-tert-butyl peroxide and a total of 9332.6 g (95.2 mol) of maleic anhydride was added over a period of twelve hours. The reaction was then heated to 190ºC over a period of two hours so that the non- reacted di-tert-butyl peroxide decomposed. Unreacted maleic anhydride was removed under vacuum (1241 Pa (0.18 psia)) at 190°C for one hour. The product was filtered to give a polyisobutenyl succinic anhydride having a saponification number of 94.5 mg KOH/g sample, 65.4 wt.% active ingredients and an average of about 1.92 succinic groups per polyisobutenyl residue. The polyisobutene was about 62.3 percent converted.

Example 3 (comparison)

This example shows that a one-step thermal reaction of polyisobutene and maleic anhydride does not yield an alkenylsuccinic anhydride in which the extent of multiple addition is higher than 1.2 succinic groups per alkenyl residue.

3000 g (2.31 moles) of polyisobutene having a number average molecular weight of 1300 and a methylvinylidene isomer content of about 6% was placed in a reactor and heated to 232°C. The pressure was 160.6 kPa (24 psia (9.3 psig)). 1083 g (11.05 moles) of maleic anhydride was added. The reaction vessel was heated to 232°C for a period of 4 hours. The excess maleic anhydride was then removed under vacuum. The product was filtered to give a polyisobutenyl succinic anhydride having a saponification number of 70.1 mg KOH/g sample, 77.2 wt.% active ingredients and an average of about 1.09 succinic groups per polyisobutenyl moiety.

Claims (13)

1. A process for preparing an alkenyl-substituted succinic anhydride, wherein the alkenyl substituent has a number average molecular weight of 500 to 5000 and an average number of succinic groups per alkenyl group of more than 1.2, comprising: (a) reacting a polyolefin having an alkylvinylidene isomer content of less than 10 percent and a number average molecular weight of about 500 to 5000 with maleic anhydride in the presence of a free radical initiator at a temperature of 100°C to 220°C to provide a mixture of alkenylsuccinic anhydride having an average of more than 1.2 succinic groups per alkenyl group and unreacted polyolefin, whereby the conversion of the polyolefin is from 30 to 65 percent, and (b) reacting the mixture of alkenyl succinic anhydride and unreacted polyolefin with maleic anhydride at a temperature of 200°C to 250°C, thereby providing an alkenyl succinic anhydride having an average of more than 1.2 succinic groups per alkenyl group and the overall conversion of the polyolefin is 5 to 40 percentage points higher than the conversion in step (a), where the alkylvinylidene isomer has the formula: wherein R₁ is a lower alkyl group having 1 to 6 carbon atoms and R₂ is a polyolefin group. 2. The process of claim 1, wherein the alkenyl succinic anhydride prepared in step (a) or step (b) has an average of more than 1.3 succinic groups per alkenyl group. 3. The process of claim 2, wherein the alkenyl succinic anhydride prepared in step (a) or step (b) has an average of more than 1.3 to 4.0 succinic groups per alkenyl group. 4. The process of claim 3, wherein the alkenyl succinic anhydride prepared in step (a) or step (b) has an average of more than 1.3 to 2.5 succinic groups per alkenyl group. 5. The process of claim 1, wherein the polyolefin has a number average molecular weight of 700 to 3000. 6. The process of claim 5, wherein the polyolefin has a number average molecular weight of 900 to 2500. 7. The process of claim 1, wherein the polyolefin is a polybutene or polypropylene. 8. The process of claim 7, wherein the polyolefin is a polyisobutene. 9. The process of claim 8, wherein the polyisobutene has a number average molecular weight of 900 to 2500. 10. The process according to claim 1, wherein the radical initiator used in step (a) is of the peroxide type. 11. The process of claim 10, wherein the radical initiator of the peroxide type is di-tert-butyl peroxide. 12. The process of claim 1, wherein the molar ratio of maleic anhydride to polyolefin in step (a) is 1:1 to 9:1. 13. The process of claim 1, wherein in step (b) 1 to 9 moles of maleic anhydride are used per mole of the mixture of alkenyl succinic anhydride and unreacted polyolefin from step (a).